ESI is a widely used field desorption ionization method that generally provides a means of generating gas phase ions with little analyte fragmentation (see, e.g., Fenn et al., Science 1989 246: 64-70). Furthermore, ESI is directly compatible with on-line liquid phase separation techniques, such as high performance liquid chromatography (HPLC) and capillary electrophoresis systems.
Increasing the sensitivity of electrospray ionization is desirable. Most developments in this area have focused on solvent and electrolyte composition, better drying, better nebulization or better ionization efficiency by miniaturization (e.g., by nanospray). This disclosure provides an alternative way to increase the sensitivity of electrospray ionization that uses a mixture of solvents.